To the OP:
If you want to be able to fly family members around North America on points, you cannot do much better than AC*SE. You have access to every seat, Y and J, at Classic levels, especially if you want to be able to book these flights last minute.
If you are generally satisfied with the service, schedule, and other SE benefits, it isn't really clear that changing airlines would be your optimal decision.
When you say "racking up 200-350k points", do you mean flying 200-350k status miles, or accumulating that many points to redeem through flying, bonus miles, and credit card miles? If you are flying over 300k and (again) want to fly family around on points, you will have been able to gift E and SE to family members along the way, making life quite comfortable for everyone.
Or, if you are flying that much, you could earn top tier on multiple airlines and alliances. But no airline program in the world has redemption abilities that even approaches AC*SE (even though they took away international J).
If you are flying 100k and earning redeemable miles to make 200-350k, you would only be able to make one top tier or two middle tiers. You could choose to earn in US or UA and use those points to redeem in Canada on AC through Star Alliance awards, but of course if you are regularly encountering Classic Plus redemption levels (because the AP website is so messed up it won't recognize your SE status properly) then you aren't going to see those flights available for Star Alliance redemptions either.
So you need to tell us more in order for good advice to be given. How do you generally feel about AC and what do you want to get out of a frequent flyer program?
There are plenty of people here who will be itching to advise you to jump ship. I'd suggest considering your options very carefully before being dragged down in others' bitterness.